Printed circuit boards for electronic equipment are provided with contact tabs disposed along one or more sides of their perimeter; such contact tabs require a surface gold-plating for satisfactory passage of current and to prevent oxidation of the contact tabs. To this end, an apparatus is provided for the sequential action of a plurality of chemical and electrochemical baths; these strip the tin-lead protective coating from the area of the circuit to be gold-plated and applying a nickel coating which imparts sufficient hardness to the contact tabs, and then apply the gold-plating in constant thickness to the contact tabs.
For this purpose use can be made of separate baths and tanks, which however makes the equipment bulky and requires much manpower, or continuously operating machines. Such machines have a number of problems, including excessive overall length to provide a sufficient output, the difficulty of effecting a dependable cathodic contact and the seal of the modules in the areas traversed by the circuit boards. The cathodic contact is usually effected by contact clips which run along the whole length of the machine; in such case, however, the contact clips must be restored to their initial position which is difficult. Alternatively, contact is effected by brushes sliding against the printed circuit boards which can damage said printed circuit boards with their continuous rubbing. The seal of the modules is usually made by means of rubberized gaskets; this type of seal, however, does not wholly prevent losses and leaks of liquid.